or       (25)

Substituting for (P_x) from equation (25) in equation (24),

                 (26)

              Let               w =

Then                 or    

Furthermore, when x=0, then and when w = L, then .

Substituting for and  (dx) in  equation (26) and inserting the new limits and integrating,

                       

 or             

Thus,                                                   (27)

Thus, the complete HETP equation for a packed GC column, that takes into account the compressibility of the carrier gas, will be

         (28)